A119044 - OEIS

%I #12 Sep 08 2022 08:45:25

%S 1,4,18,58,59,141,471418,185310604,451023506,1184061400,1844511706,

%T 4474395400,14266749459,18444896915,48521543066,11838218371106,

%U 39270880053981

%N Numbers k such that the k-th triangular number contains only digits {0,1,7}.

%C Next term exceeds 1.4*10^16.

%H G. Resta, <a href="http://www.numbersaplenty.com/tr/tr017.html">Tridigital Triangular Numbers</a>

%t Select[Range[3 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {0, 1, 7}] == {} &] (* _Vincenzo Librandi_, Oct 06 2015 *)

%o (Magma) [n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1,2))) subset [0,1,7]]; // _Vincenzo Librandi_, Oct 06 2015

%Y Cf. A000217, A119043. See A119034 for a table of cross-references.

%K nonn,base,more

%O 1,2

%A _Giovanni Resta_, May 10 2006